This paper extends the single-currency LMM to the cross-currency LMM based on the Amin and Jarrow (1991) framework, and the resulting model is applied to deriving the approximate pricing formula of the quanto average interest options via two different approximation approaches, presented by Vorst (1992) and Levy (1992). These two approximation formulas have been examined to be very accurate as compared with Monte Carlo simulation. The model calibration procedure is also presented in detail for practical implementation.